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I agree with Mr. Pipes. I’ve not used that API ever and I’ve no recollection of anyone asking about it nor am I aware of anyone who actually uses it. I vote to deprecate.

-----Original Message-----
From: Jay Pipes <jaypipes at gmail.com>
Date: Saturday, April 1, 2017 at 10:02 AM
To: "openstack-operators at lists.openstack.org" <openstack-operators at lists.openstack.org>
Subject: Re: [Openstack-operators] [nova] Can we deprecate the os-hosts API?

    My vote is to deprecate it.
    
    On 03/22/2017 11:16 AM, Matt Riedemann wrote:
    > This is mostly directed at operators but I'm cross-posting to the ops
    > and dev lists.
    >
    > First, does anyone use the os-hosts API and if so, for what use cases?
    >
    > The os-hosts and os-services APIs are very similar, and they work on the
    > same resources (the 'services' records in the nova database).
    >
    > Both APIs allow you to list services and show details for a specific
    > service.
    >
    > Both APIs allow you to enable and disable a service so instances will
    > not be scheduled to that service (compute host).
    >
    > There are some additional 'action' APIs that are specific to the
    > os-hosts API, which are:
    >
    > 1. Putting the service (host) into maintenance mode. This is only
    > implemented by the XenServer virt driver and despite the description in
    > the support matrix [1] I'm told that it doesn't actually evacuate all of
    > the guests from the host, it just sets a flag in the Xen management
    > console, and is therefore pretty useless. Regardless, we have other APIs
    > that allow you to do the same thing which are supported across all virt
    > drivers, which would be disabling a service and then migrating the
    > instances off that host.
    >
    > 2. Reboot host. This is only supported by the XenServer and Hyper-v
    > drivers. This is also arguably something that does not need to live in
    > the compute API. As far as I know, the backing drivers do no
    > orchestration of dealing with guests in the nova database when
    > performing a reboot of the host. The compute service for that host may
    > be temporarily disabled by the service group health check which would
    > take it out of scheduling decisions, and the guests would be down, but
    > the periodic task which checks for unexpectedly stopped instances runs
    > in the nova-compute service, which might be dead now so the nova API
    > would show the instances as running when in fact they are actually stopped.
    >
    > 3. Shutdown host. Same as #2 for reboot host.
    >
    > 4. Start host. This is literally not supported by any in-tree virt
    > drivers. The only drivers that implement the 'host_power_action' method
    > are XenServer and Hyper-v and they do not support the 'startup' action.
    > Since this is an RPC call from nova-api to nova-compute, you will at
    > least get a 501 error response indicating it is not supported or
    > implemented (even though 501 is the wrong response for something like
    > this).
    >
    > --
    >
    > So is anyone using any of these APIs? As noted, only Xen users can use
    > the maintenance mode API but I'm told it's useless. Which leaves the
    > stop/reboot power action APIs, which are only for XenServer and Hyper-v.
    > Are there any users of those drivers that use those APIs and if so, why?
    >
    > If no one uses any of those power action or maintenance APIs, then we
    > propose to deprecate the os-hosts API. The list/show/enable/disable APIs
    > are already covered by the os-services API which we actually intend to
    > improve [2] so those would be the replacement.
    >
    > [1]
    > https://docs.openstack.org/developer/nova/support-matrix.html#operation_maintenance_mode
    >
    > [2] https://review.openstack.org/#/c/447149/
    >
    
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